Images of the topology of the eyeground (retina or fundus) are important for the diagnosis of many eye diseases. Many of the diseases of the retina can be examined more precisely with the accurate use of diagnostic lasers and treated with the precisely accurate application of therapy lasers.
In the prior art, numerous and diverse solutions are known for the observation, diagnosis, and therapy of the eye. Therein, the required images are produced, e.g., with hand-held ophthalmoscopes, slit lamps, fundus cameras, or laser scanning ophthalmoscopes.
Fundus cameras are one of the most important diagnostic instruments in ophthalmology. With their help, it is possible to map wide field images of the eye fundus and deduce diagnoses therefrom.
In [1], R. F. Spaide describes special embodiments, with which it is possible to apply functional types of diagnoses beyond the mere evaluation of the RGB image (red, green, blue).
For example, in U.S. Pat. No. 7,134,754 B2, a retinal function camera is described, which includes two laser light sources with different wavelengths. Thereby, the wavelength bands are selected in such a way that the absorptivity of light of the first wavelength band is greater with oxygenated blood and the absorptivity of light of the second wavelength is greater with deoxygenated blood; as a result, respective images can be produced and analyzed.
Hence it is possible to diagnose even early stages of macular atrophy, which causes age-related loss of photoreceptor cells and retinal pigment epithelium and leads to gradual loss of detailed central vision.
However, with the described solution, the forming of choroidal neovascularization in early stages can also be detected. These small, new, anomalous blood vessels grow and proliferate from the choroid layer and can cause acute loss of vision if blood collects in or below the retina. The diseased spots made visible with the described solution can be treated either with photo coagulation of by application of photodynamic therapy.
A fundus camera, which also includes the use of two laser light sources with different wavelengths, is described in U.S. Pat. No. 7,198,367 B2. Thereby, however, the wavelength bands are chosen in such a way that fluorescence images of the fundus can be mapped and analyzed in the visible as well as the infrared range.
However, the currently known functional diagnoses with a fundus camera are still based on the principles of the wide field illumination. A more complex diagnosis, which takes place in individual spots on the retina, such as perimetry, optical coherence tomography or a precisely accurate therapy through coagulation, is still not possible with said system.
Furthermore, laser scanning ophthalmoscopes have also become established in ophthalmology. Hereby, a laser beam is usually mapped confocally onto the retina via a mechanical scanner, e.g., a galvanometer scanner or a polygon mirror. The light returned from the retina in the mapped spot is detected by a sensor inside the device.
The information about the topography of the retina is gathered through scanning with the help of the scanner. With laser scanning ophthalmoscopes it is possible to perform a precisely accurate therapy or diagnosis of the retina. In a conventional laser scanning ophthalmoscope, the laser serves as light source for imaging as well as for diagnosis and/or therapy.
However, since the eye of a patient can move during observation relative to the ophthalmoscope, it is necessary to constantly observe the topography of the eye fundus. For that reason, resonantly driven scanners, which continuously scan the retina, are used in all known laser scanning ophthalmoscopes. A precisely accurate therapy or diagnosis is only possible when the scanner is aligned in such a way that the laser point covers exactly the desired spot on the retina. Therefore, an elaborate synchronization between scanner and the therapy or diagnostic laser is required.
In order to avoid exceeding the maximum admissible impulse energies during treatment, it is necessary to control the resting time of the scanning laser beam, depending on its intensity, through an elaborate positioning device and an intensity monitor. For example, in WO 2004/043234 A1, an optimized laser scanning ophthalmoscope is described, wherein a confocal laser scanning laser ophthalmoscope and external laser sources are combined in order to simultaneously observe and treat the same spot on the retina.
Thereto, EP 1 308 124 A2 describes a lens system for the use with a laser scanning ophthalmoscope. The described lens system realizes a very broad wide field, so that areas of the eye can be examined by the laser scanning ophthalmoscope which are ordinarily inaccessible.
A further laser scanning ophthalmoscope is described in U.S. Pat. No. 6,337,920 B1. The laser scanning ophthalmoscope (LSO), which consists of a laser-beam producing laser light source, a first scanning device for producing an oscillating beam deflection in a first direction, and a second scanning device for producing an oscillating beam deflection in a second direction, also contains detection devices for detecting the light reflected from the eye.
From the fundus image produced by a first scan of the retina, sub-areas of the fundus can be selected, onto which a second scan can be focused, particularly, refined. Thereby, the individual scanning devices are independently swivel-mounted via drive motors controlled by an activation device.
DE 38 36 860 C2 describes an ophthalmological device with laser beam scanning. This solution also uses two wavelengths. While one laser beam is utilized for coagulation/excitation of the fundus, the other laser beam is used for scanning imaging of the fundus, whereby both laser beams are utilized parallel and simultaneously. This solution provides an ophthalmological device with laser beam scanning with which a designated spot of the fundus can be marked on the screen and an adequate image of said spot produced.
A third option for simultaneous imaging of the eye fundus and application of therapy lasers on the retina consists of the use of slit lamps. However, in order to position said slit lamps precisely, a fixation of the eye is required. A fixation is usually achieved through a contact glass. The contact glass also serves as compensation for the refractive power of the eye.
Thereby, it is disadvantageous that the laser coagulation with a slit lamp requires a contact glass, and its reproducibility is extremely low.
Furthermore, the accuracy of positioning the laser spot on the retina depends greatly on the operator since a precisely accurate therapy or diagnosis is only possible if the scanner is aligned in such a way that the laser spot covers exactly the desired spot on the retina. Thereto, elaborate synchronization between scanner and the therapy or diagnostic laser is absolutely necessary. In order to avoid exceeding the maximum admissible impulse energies during treatment, it is necessary to control the resting time of the scanning laser beam on the interesting spot, depending on its intensity, through elaborate positioning devices and an intensity monitor.
The method as well as the respective device described in WO 2007/035855 A2 are based on the principle of a slit lamp, which was expanded with a scan unit in order to execute a pattern-assisted laser coagulation on the retina. This, however, requires the positioning of a contact glass on the patient's eye, with which the refractive power of the eye is compensated and/or a beam shaping of the laser for coagulation is performed. In addition, only a local therapy of the retina is possible due to the very small observation area when compared with the fundus camera. This is caused by the basic design of a slit lamp. In order to treat larger areas of the retina, the eye of the patient must be moved or special contact glasses must also be applied.
Moreover, it is not possible to perform a fundus image-based positioning for the coagulation laser as well as document the set coagulation points. Diagnostic procedures, such as perimetry, fluorescence imaging, spectroscopic analyses, or optical coherence tomography are also impossible.